A muzzle-loading firearm is a firearm in which the projectile and propelling charge is loaded through the muzzle (i.e. the front-end of the barrel), in contrast to a breech-loading firearm in which the projectile and propelling charge is loaded through the breech, or rear end, of the barrel.
Muzzle-loading firearms typically have a barrel with an attached breech plug. In some muzzle-loading firearms the breech plug is permanently attached, and in others it is removable. Removable breech plugs facilitate pass-through cleaning of the bore of the barrel. Removable breech plugs also facilitate unloading, and clearing a miss-fire in the firearm.
Many prior art removable breech plugs are externally-threaded, and as such, they thread into the barrel of the firearm. In these systems, the barrel is internally-threaded to accept the threaded breech plug. Internally-threaded barrels create several problems including a potential for fouling of the threads during cleaning of the bore. This can make the breech plug difficult or impossible to reinstall or remove. Externally-threaded breech plugs are also generally larger in diameter than the bore of the barrel so that there is a tight seal when the breech plug is installed. The thickness of the barrel wall surrounding the plug is often thinner than the barrel wall just in front of the plug, which can create a strength limitation in the barrel and a risk of expansion. If a thicker barrel wall is then required, it can increase manufacturing cost and/or the weight to the firearm.
In externally-threaded breech plug systems, the barrel must be designed to retain the externally-threaded breech plug even in overpressure circumstances. The barrel must have adequate thickness to resist excessive expansion in such extreme circumstances to ensure that the barrel's internal threads do not fail to retain the plug. Further, the length of the externally-threaded breech plug must be long enough to provide adequate strength to retain the pressure necessary in the chamber. Thus, the length of the externally-threaded breech plug extends the length of the barrel of the firearm without extending the length from the breech face to the muzzle. The added barrel length increases the weight and cost of the firearm without the performance advantages of a lengthened barrel.
In other firearms with removable breech plugs, such as in the Harrington & Richardson 45, the breech plugs are push in breech plugs. The push in breech plugs are sealed with a neoprene O-ring, or a nylon ring. These push in breech plugs are removable by opening the breech and pushing out the plug with a ram rod. The push-in breech plugs are held in by friction. The push in breech plugs are considered unsafe as the breech plug is only secured when the breech is closed. If one opens the breech too quickly after a misfire, and the misfire is a hang fire, the expulsion of the pressurized gases would make serious injury likely.
In other prior art muzzle-loading firearms, there is no breech plug. Instead, an internally-threaded breech cap is threaded onto the externally-threaded barrel of the firearm, and the base of the breech cap overlays the face of the rear end of the barrel. In the area of the base of the breech cap which overlays the end of the barrel, there is a central axial cylindrical primer pocket. The floor of the primer pocket has a central fire hole that communicates with a cylindrical chamber at the rear end of the barrel. The surfaces are tightly abutted to provide a gas seal against escape of propellant gases from the chamber upon discharge.
While systems without breech plugs overcame some of the problems caused by an externally-threaded breech plug, other problems still remain. For example, there are issues in using only a breech cap to retain the gas pressure in the chamber. The area of the barrel walls where they are threaded are necessarily thinner and are subject to expansion which can make removal and reinstallation of the breech cap difficult, if not impossible.
The present invention prevents over-pressure and expansion issues by locating the muzzle end of the breech plug forward of the threaded portion of the barrel where the walls of the barrel are not thinner. The present invention also minimizes the problems associated with back-pressure by providing a removable, threadless breech plug, and a breech plug retaining collar. These features allow not only for ease of manufacture and cleaning but also for preventing fouling and overpressure. The present invention solves additional problems of prior art muzzle-loading firearms by providing a barrel retaining nut. This feature allows for ease of manufacture, finishing and cleaning and prevents fouling. The removable, threadless breech plug further allows for the interchangeability of breech plugs to accommodate a variety of different primers and propellants thus improving the usability and accuracy of the firearm.